This invention involves a modem which receives a series of bits from a data source for transmission. The data bits are then arranged into groups of bits each group defining a transmitted point or symbol. The size of each group depends on the type of modulation used. For example, if the data rate is 4800 b/s and 8-point QAM is used then each group is formed of three bits. Next, each group of bits is translated into one of the QAM points and then transmitted. At the receiver end the process described herein is reversed.
Thus, for example, if the modem is capable of transmitting 1,600 symbols/sec., its transmission rate is 4,800 bits/sec. Such modems are well known in the art.
The inventors have found that the capability of such modem can be further increased in the manner described below.